Phenol is commercially manufactured by any one of seven different processes. The seven processes used to manufacture phenol involve different aromatic starting materials and generally involve a step requiring an acid catalysis, an acidification, or the formation of an acid by-product. The six processes are: 1) decomposition of cumene hydroperoxide, 2) benzoic acid decarboxylation, 3) decomposition of sodium phenolate produced by sulfonation, 4) decomposition of sodium phenolate produced by alkaline hydrolysis of chlorobenzene, 5) catalytic hydrolysis of chlorobenzene, 6) dehydrogenation of cyclohexanol, and 7) BPA by-product cracking. These seven processes are hereinafter discussed to demonstrate the general applicability of the present invention.
Decomposition of cumene hydroperoxide
Briefly summarized the decomposition of cumene hydroperoxide comprises alkylation of benzene to cumene, oxidation to cumene to cumene hydroperoxide, followed by cleavage of cumene hydroperoxide to phenol and acetone. A typical process will involve the use of three or four cumene oxidation reactors in series. Fresh and recycled cumene is fed to a first reactor and air or oxygen is bubbled into the bottom of the reactor and exits at the top. If a reaction promoter is used there may be a layer of 2-3% aqueous sodium hydroxide in the bottom of the reactor. The reaction temperature decreases through the reactor series from about 115.degree. C. to 90.degree. C. in the last reactor. Generally the conversion in the first reactor is 9-12%, that in the second 15-20%, that in the in the third 24-29%, and in the last 32-39% with an overall yield through the reactor train of 90-95% by weight. The residence time in each reactor is roughly 3-6 hours. The cumene hydroperoxide is concentrated by evaporation to a solution that is 75-85 wt. % cumene hydroperoxide. Unreacted cumene hydroperoxide is recovered by distillation and recycled to the first reactor.
Cleavage of cumene hydroperoxide occurs under acidic conditions with agitation at a temperature of 60.degree.-100.degree. C. using various non-oxidizing inorganic acids or acid anhydrides, e.g. sulfur dioxide (hydrolyzed to sulfurous acid). Since phenols are inhibitors for free-radical oxidation processes, it is essential that no acidic materials interfere with the oxidation process. The solution in the cleavage reactor is a mixture of phenol, acetone, and various by-product compounds such as cumylphenols, acetophenone, dimethylphenylcarbinol, and .alpha.-methylstyrene. The resulting solution may be neutralized with a sodium phenoxide solution, another suitable base or passed over an ion-exchange resin. Process water may be added to assist in the removal of inorganic salts resulting from the neutralization of process acid or acid by-products. The resulting product may then be separated, washed and/or directly distilled.
Decomposition of benzoic acid
Toluene is oxidized to benzoic acid by a liquid phase free radical oxidation. After purification, the resulting benzoic acid product is decarboxylated or oxydecarboxylated to phenol either as the molten benzoic acid or in a high boiling solution, typically with a solvent boiling in the range of 220.degree.-250.degree. C. in the presence of steam and air and a suitable catalysts, typically a copper salt catalyst. Variations on this process exist such as a vapor-phase oxidation of benzoic acid over a copper catalyst to produce the phenol directly.
De-sulfonation of benzene sulfonic acid (decomposition of sodium phenate)
Benzene is sulfonated with sulfuric acid at a temperature of 110.degree.-150.degree. C. with an excess of sulfuric acid followed by neutralization of the resultant benzenesulfonic acid with alkali, usually sodium hydroxide. The benzenesulfonic acid is decomposed in molten sodium hydroxide at 320.degree.-340.degree. C. to form sodium phenolate. Treatment with sulfur dioxide forms sodium sulfite and releases phenol.
Hydrolysis of chlorobenzene
Benzene is chlorinated in a liquid phase catalytic chlorination employing ferric chloride as the chlorination catalyst at temperatures ranging from 25.degree.-50.degree. C. The resultant chlorobenzene is hydrolyzed using a caustic solution of 10-15 wt. % sodium hydroxide at temperatures ranging from 360.degree.-390.degree. C. under high pressure, 280-300 atm (28-30 MPa). Hydrogen chloride (hydrochloric acid) releases the phenol from the sodium phenate (phenolate).
Catalytic hydrolysis of chlorobenzene
A variation of the chlorobenzene process involves the synthesis of chlorobenzene by a catalytic oxychlorination over a cupric chloride, ferric chloride on alumina catalyst using air hydrogen chloride mixtures. The resulting chlorobenzene is catalytically hydrolyzed over a silica supported calcium phosphate catalyst under reducing conditions obtained by the presence of hydrogen at temperatures of 400.degree.-450.degree. C.
Cyclohexanol dehydrogenation--Cyclohexane is oxidized to cyclohexanol and cyclohexanone followed by catalytic dehydrogenation over a group VIII metal catalysts such as platinum on activated carbon or nickel cobalt on alumina. The phenol product, which forms an azeotropic mixture with cyclohexanone, is separated by an extractive process such as liquid-liquid extraction. By comparison to the previous five processes, this process has very unfavorable process economics and is no longer employed commercially to any great extent. Of the seven processes, this process is the only process where acid workup or catalysis by acidic species such as the Bronsted acids sulfuric and hydrochloric acids or the Lewis acids such as ferric chloride and the like is not employed.
Cracking of By-Products from Bisphenol Manufacture
In the process of manufacturing various bisphenol compounds by-products result therefrom. These by-products are typically recycled to a cracking reactor where they are reconverted to the phenolic precursors. Cracking of bisphenol by-products typically involves catalysis by strong acids or bases. Generally, strong acid cracking gives better yields of the phenolic compounds desired. The cracking process is generally conducted at temperatures ranging from 150.degree. to 400 .degree. C. This cracking process does not synthesize phenol directly but cracks the products synthesized from phenol back to phenol.
The six commercially significant processes all employ either a Bronsted acid or a Lewis acid in the reaction scheme to produce phenol. The Bronsted acids such as sulfuric acid, arylsulfonic acids, or hydrochloric acid may leave direct contaminating trace quantities in the process stream. The Lewis acids such a ferric chloride, zinc chloride, cupric chloride, aluminum chloride, and the like suffer hydrolysis forming Bronsted acids, e.g. hydrochloric acid, that again may directly contaminate the process stream. Further when ion-exchange resins are utilized anywhere in the process, decrepitation of the resin has been observed leading to a contamination of the process stream downstream of the ion-exchange resin bed by a polymeric acidic resinous material. The presence of acids in phenol catalyze undesired decomposition and by-product reactions in further downstream processing such as distillation. The presence of trace quantifies of acids in phenol may persist beyond the use of phenol as a reagent and subsequently also catalyze undesired reactions in the product materials that are subsequently synthesized therefrom. Therefore, it is desirable to remove the various acidic components present in phenol process streams before undesired reactions are catalyzed thereby.